feat: Implement return and refund functionality in commerce module

- Added return request handling in return.controller.js
- Implemented webhook handling for PayHere payments in webhook.controller.js
- Created models for coupon redemptions, invoices, orders, order items, payments, payment attempts, payment webhook events, refunds, return items, and return requests.
- Developed services for order management, payment processing, refunds, and returns.
- Introduced validation schemas for payment and return requests.
- Created migration scripts for new database tables related to orders, payments, refunds, and returns.
- Added unit tests for order state transitions and PayHere provider functionality.

app/models/commerce/refundItem.model.js

@@ -0,0 +1 @@
+module.exports=(s,D)=>s.define("RefundItem",{id:{type:D.STRING,primaryKey:true},refund_id:{type:D.STRING,allowNull:false},order_item_id:{type:D.STRING,allowNull:false},quantity:{type:D.INTEGER,allowNull:false},amount:{type:D.DECIMAL(15,2),allowNull:false}},{tableName:"refund_items",timestamps:true});